PALEOMAGNETISM OF THE MISSISSIPPI VALLEY-TYPE NEWFOUNDLAND ZINC DEPOSIT - EVIDENCE FOR DEVONIAN MINERALIZATION AND HOST ROCK REMAGNETIZATION IN THE NORTHERN APPALACHIANS

Newfoundland Zinc Mines (NZM) are exploiting sphalerite-rich Mississip pi Valley-type (MVT) zones in platformal carbonate rocks of the Humber Zone in western Newfoundland. The zones are stratabound within the up per part of the Lower Ordovician St. George group. Geologic studies in the mine area simply require ore genesis to postdate the Early to Mid dle Ordovician Taconic orogeny. Thermal and alternating field (AF) dem agnetization reveal that both the ore and adjacent host rocks at the N ZM have similar characteristic remanence magnetizations (ChRM) with no rmal polarity. The ChRM direction from both ore and host rocks is at 9 -degrees/-30-degrees (declination/inclination) (N = 16 sites, alpha95 = 6-degrees, k = 46) which gives a pole position of 22-degrees-N, 113- degrees-E (dp = 3-degrees, dm = 6-degrees). This pole falls on the bou ndary between the Middle and Late Devonian on the North American appar ent polar wander path and corresponds in time to the Acadian orogeny. Paleomagnetic breccia tests show that the host rocks were remagnetized after the Middle Ordovician and that this remagnetization coincides w ith or postdates MVT mineralization. The ChRMs paleoinclination indica tes that both remagnetization and mineralization are not younger than Late Devonian. The similar magnetization characteristics of the adjace nt and remote host rocks in the Humber Zone and the authigenic nature of the magnetic carriers revealed by scanning electron microscopy with energy dispersive analysis suggest that the NZM host rock has a secon dary magnetization. From the pervasive nature of both the secondary re magnetization and the trace MVT mineralization in the northern Humber Zone, we argue that both events are coeval. We suggest that Acadian or ogenic uplift forced hot basinal brines into the porous and fractured Ordovician shelf carbonates of the northern Humber Zone.